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/A newsletter about soil, sediment, and groundwater characterization and remediation technologies
Issue 44
;s.rae of Technology News and Trends highlights approaches to assessing,
mitigating, and monitoring vapor intrusion (VI). Varied action levels for VI repre-
sent varying site-specific factors included in development of the action level.
EPA Studies Identify Techniques for Critical Leak Testing Prior
to Soil-Vapor Sampling
Researchers at EPA's National Risk
Management Research Laboratory
(NRMRL) in Ada, OK, are developing
quality assurance (QA) measures for
soil-gas and sub-slab sampling methods
that help differentiate contaminant vapors
due to vapor intrusion from background
sources. Recent research focused on
measures to identify leakage of ambient
air into conventional vapor probes, which
can significantly impact sampling results.
During sub-slab or soil-gas sampling,
ambient air may enter the sampling vessel
(e.g., sampling bag or canister) through
loose fittings connected to the probe or
through openings or cracks in the
concrete and bentonite seals used to
isolate screened intervals. If leakage
occurs and gas concentrations at the
point of leakage are less than soil-gas
concentrations, concentrations measured
in a sampling vessel will be less than true
concentrations in the subsurface. In the
absence of leak testing, leakage is
assumed to have occurred if anomalous
results are observed; otherwise,
measurements are assumed to be valid.
The QA measures for soil-gas leak
detection involve use of a small, sealed
chamber that can be integrated into an
above-ground sampling train. Placement
of the chamber directly on top of a sub-
slab or soil-gas probe enables each
component of the sampling train to be
vacuum or pressure tested with a gas
tracer such as helium (He). Valves or gas-
tight, quick-connect fittings are used to
isolate each component during testing and
containerize the vapor.
To test integrity of fittings for the leak
detection chamber, NRMRL used a
peristaltic pump to create a vacuum of
97.3 kPa in the flowmeter and tubing of
a laboratory-deployed sampling train.
The vacuum was initially recorded every
second and then relaxed to every 120
seconds as it gradually dissipated over 35
hours. The Ideal Gas Law was used to
calculate flow rate into individual
components of the sampling train.
Results indicated nearly a complete
vacuum, with leakage of only 0.72
standard cubic centimeters per minute.
NRMRL considers leakage less than 1%
of the flow rate to be insignificant and
below the detection limit.
Similar QA measures can be used in the
field to leak test boreholes. One method is
to flood the detection chamber surrounding
the top of a borehole with a gas mixture
containing a tracer (usually He).
Concentrations in the chamber and line or
in the sampling vessel are then monitored.
Typically, He is injected into the chamber
as a pure gas, and a portable thermal
conductivity detector (TCD) is used to
monitor the sampling train. The density of
dry, pure-phase He is only 0.16 g/L at 20°C,
while the density of soil gas typically
exceeds 1.2 g/L. As a result, pure-phase
He is buoyant and will not be drawn down
[continued on page 2]
September 2009
Contents
EPA Studies Identify
Techniques for Critical
Leak Testing Prior to
Soil-Vapor Sampling page 1
Vapor Intrusion
Mitigated Through
Solar-Powered
Exhaust Systems page 2
Proposed Plan Offers
Tiering Systems to
Determine Preferred
Alternatives for Vapor
Intrusion page 4
Program Developed
to Ensure Long-Term
O&M and Performance
of Vapor Intrusion
Mitigation page 4
New Approaches
Studied to Investigate
Vapor Intrusion
page6
Online Resources
The vapor intrusion "Issues"
area of CLU-IN provides an
information compendium
including EPA's 2008 Engi-
neering Issue: Indoor Air
Vapor Intrusion Mitigation
Approaches, the Interstate
Technology and Regulatory
Council's 2007 Vapor Intrusion
Pathway: A Practical Guide-
line, and the 2008 Detailed
Field Investigation of Vapor
Intrusion Processes report
developed under the U.S.
Department of Defense
Environmental Security
Technology Certification
Program. Access these
documents at: www.cluin.org/.
Recycled/Recyclable
Printed with Soy/Canola Ink en paper that
contains at least 50% recycled fiber
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[continued from page 1]
a compromised borehole without
sufficient vacuum in a screened interval.
NRMRL developed a heuristic model
(Figure 1) to provide a conceptual
understanding of borehole leakage. Only
vertical compressible gas flow is allowed
down a compromised borehole having
an integrated gas permeability of kr The
integrated permeability of the borehole
incorporates the presence of cracks and
openings in and around an essentially
impermeable matrix of concrete and
bentonite. Only radial compressible flow
is allowed to a screened interval in a
homogeneous isotropic medium having
a gas permeability of kr
These calculations indicate that leakage
is primarily a function of the permeability
contrast between the formation and
borehole. As the ratio of formation to
borehole permeability decreases, the
potential for leakage increases. The
potential for leakage then is greatest in
soil having low gas permeability.
The leak detection chamber was
integrated into a borehole sampling train
used to evaluate past releases from
underground storage tanks at an
automotive station in Green River, UT.
Onsite soil consists primarily of clay,
and the soil gas consists of 79.8% N2
and 20.2% 02, with a calculated density
of 1.19 g/L at 20°C and 100% relative
humidity. To minimize the effect of
buoyancy, a gas mixture of He and
argon (Ar) was injected to achieve a
near-constant gas mixture inside a
chamber of 42% Ar, 21% He, 7.8%
oxygen (02), and 29.2% nitrogen (N2)
with a calculated gas density of 1.15 g/L
at ambient temperature. A portable
TCD and landfill gas meter were
used to measure He and 02, carbon
dioxide and methane in the sampling
train and specifically within the
chamber, respectively. QA tests
indicated nearly 100% leakage in the
borehole, which in turn prompted
evaluation of whether to redesign or
abandon the borehole.
NRMRL recommends that leak testing
always precede soil-gas sampling,
especially in media of lower permeability,
until the integrity of a borehole is well
established. All components of the
sampling train should be vacuum or
pressure tested with quantified flow into
or out of the system prior to sample
collection. For leak testing of conventional
probes, a chamber containing a gas
mixture approaching the density of soil gas
should be used, and tracer concentrations
in the chamber should be held constant in
order to quantify the leakage.
NRMRL has developed purge and
transient gas permeability test measures
that can be used simultaneously with
the leak detection methods. The
concurrent testing process relies on
multiple tracers introduced into multiple
intervals of soil-gas probe clusters.
Contributed by Dominic Digiulio,
NRMRL (digiulio.dominic(a),epa.gov
or 580-436-8605)
Air extraction
z=°
Leaka9e=TTAlk7k7
where A is a geometric constant defined by
A=^r7T)
and L is the length of concrete and bentonite seal
z=L
Open boundary
Figure 1. NRMRL's conceptual
model and formula can be used
to evaluate leakage in a vapor
sampling train on a scale of 0
to 1.
Vapor Intrusion Mitigated Through Solar-Powered Exhaust Systems
EPA Region 6 undertook a Superfund
removal action earlier this year at the
Delfasco Forge site in Grand Prairie,
TX, to address trichloroethene (TCE)
vapor migrating from a groundwater
plume. Region 6 and the State had
determined after extensive site
investigations that technologies such as
soil vapor extraction or natural attenuation
would require several years to remove
or reduce the plume significantly. As
a result, the time-critical removal now
underway involves installing exhaust
systems in offsite buildings with TCE
vapor concentrations above the action
level. Long-term, inexpensive operation
of the systems is enhanced through use
[continued on page 3]
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[continued from page 2]
of solar energy to generate the
electricity needed by the exhaust fans.
From 1981 until 1997, the Delaware
Forge and Steel Company used less than
two acres of the site for metal forging
and fabrication that applied degreasing
agents containing TCE. Studies in 2003-
2005 indicated that degreaser spills and
releases had led to contamination of
shallow groundwater extending below
an adjacent 65-acre area with
approximately 500 homes and six light
industrial businesses.
Investigations conducted in 2008 for
RCRA corrective action involved
collection of soil samples, air samples
from crawl spaces and indoors, and sub-
slab soil vapor samples to assess potential
migration of contaminant vapor from the
groundwater plume, which is located 18-
32 feet below ground surface. Region 6
used EPA's TAGA van, a vehicle
equipped with a trace atmospheric gas
analyzer and summa-type canisters, to
collect and analyze the air. TCE was
detected in 18 homes with two showing
concentrations above the action level of
14 ug/m3.
Passive air sampling also was conducted
in the immediate four-block area to
further define the vapor plume. Semi-
quantitative samples were collected at
100 points over two weeks, at a unit cost
of $18. Results further defined a soil
vapor plume that is in the heart of the
known groundwater plume and lies under
approximately 12 homes.
This past January, Region 6 collaborated
with the Texas State Health Services and
the Agency for Toxic Substances and
Disease Registry to conduct indoor air
sampling in forty homes located in four
areas of Grand Prairie. The sampling
event was scheduled for mid winter, the
time of year most likely to present a
worst-case scenario of reduced
ventilation and low TCE decomposition
due to closed-up buildings. Results showed
two additional homes with air
contamination above the TCE action
level, both of which are located in the
area of the vapor plume earlier defined
through passive soil-gas sampling. The
State also collected blood samples from
residents of all 40 buildings.
Most of the homes in this neighborhood
are "pier and beam" structures with
underlying crawl spaces. This
architectural design prompted use of an
exhaust system that could evacuate air
in the crawl space and prevent TCE
buildup and additional migration into the
home's interior. The simple mitigation
design allows a commercially available fan
to be powered by a solar energy unit
(Figure 2), which saves the homeowner
an estimated $96/year for electricity.
To date, exhaust systems have been
installed in the four homes found to have
TCE concentrations exceeding action
levels. Each system consists of a
conventional 6-inch, 200-CFM fan
installed in the crawl space and is
powered by a 10- by 16-inch, 10-watt
solar panel mounted on the building's roof.
Each solar panel can be supplemented by
a 24-volt battery with a lifespan of 5-7
years to ensure continuous operation of
the exhaust system. System installation
was completed in two days, including less
than one hour for solar panel installation.
Equipment costs for each system included
$200 for the fan and the solar panel, and
$50 for the battery.
Homes with slab foundations will
require a subsurface mitigation system
involving lateral pipes between sumps
typical of radon fan systems. Project
plans estimate that each subsurface
exhaust system will employ a 65-watt
radon fan operating at a rate of 200
CFM and powered by a 36- by 36-
inch solar panel. A subsurface system
can be installed within 10 days.
Equipment costs are anticipated to
include $1,500 for each radon fan and
$800 for each panel.
Post-installation sampling of two exhaust
systems indicated an immediate 95%
reduction in TCE vapor in each
building's interior. Exhaust systems will
be offered this fall to 10 additional homes
in the area defined by soil-gas sampling.
If additional homes are found above the
action level, exhaust fan systems will be
offered to the homeowners.
Contaminant migration from the
Delfasco Forge groundwater plume is
expected to continue for up to 30 years.
As a result, Region 6 is gathering
information to evaluate the site's
potential inclusion on the National
Priorities List (NPL).
Contributed by Greg Fife, EPA
Region 6 (fife. greg(a),epa. gov or
214-665-6773)
Figure 2. Each
photovoltaic panel
for the Delfasco
Forge offsite VI
mitigation project
was installed at a
25-50° tilt with
unobstructed
southern exposure
to the sun.
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Proposed Plan Offers Tiering Systems to Determine Preferred Alternatives for Vapor Intrusion
EPA Region 9 has issued for public
comment a proposed plan to mitigate
VI in commercial and residential
buildings at the Middlefield Ellis
Whisman (MEW) Study Area, which
includes three NPL sites in Mountain
View and Moffett Field, CA. Formerly
used for industrial and semiconductor
activities, this area has undergone
extensive soil and groundwater
remediation to remove TCE and other
contaminants in compliance with a
1989 record of decision (ROD).
As part of a supplemental remedial
investigation from 2003-2008, over
2,800 air samples, including indoor,
outdoor, and pathway air samples,
were collected at 47 commercial and
31 residential buildings. TCE was found
to exceed EPA Region 9's TCE interim
action levels in several buildings. As a
result, discrete mitigation methods
were implemented (e.g., sealing
conduits, enhancing ventilation, and
installing sub-slab ventilation systems)
to reduce indoor air concentrations.
The proposed plan presents EPA's
preferred alternatives for protection
of building occupants from potential
long-term exposure to VI. Two tiering
systems, one for existing and one for
future buildings, are proposed.
Detailed decision trees were developed
to help assign each building a proposed
action based on sampling results.
Depending under which tier it falls,
a building may require an engineered
remedy, monitoring, and/or
institutional controls.
Following consideration of all public
comments extended through October
8, 2009, EPA will select the VI
remedy in a ROD amendment and
then work with the responsible parties
to implement the remedy. For more
information, see www.epa.gov/
resion09/MEW.
Contributed by Alana Lee, EPA
Region 9 (lee. alana(a),epa. gov or
415-972-3141)
Program Developed to Ensure Long-Term O&M and Performance of Vapor Intrusion Mitigation
EPA Region 7 has developed a
comprehensive VI program to
address the installation and long-term
operation and maintenance (O&M) of
VI mitigation systems, as well as
assessment sampling for future
systems, in homes near the Chemical
Commodities, Inc. Superfund site
(CCI). Region 7's VI Program
Implementation Manual, which
describes decision processes and
procedures as well as roles and
responsibilities for these activities, is
helping ensure protection of area
homes and information outreach to
the community.
The CCI site is an inactive chemical
recycling facility located in central
Olathe, a suburb of Kansas City. From
1951 until 1989, the facility stored and
processed a variety of chemicals
including surplus industrial and
laboratory chemicals, many of which
were hazardous substances and
wastes. Materials were stored in
aboveground and underground storage
tanks and other containers throughout
the site. Poor handling and
housekeeping practices led to spills,
leaks, and fires.
Following a fire in 1977, site
investigations found that soil and
groundwater at CCI were contaminated
with elevated levels of metals, pesticides,
PCBs, semi-volatile organic compounds,
and volatile organic compounds (VOCs).
Subsequent investigations indicate that
the groundwater contaminant plume
extends offsite, having migrated at least
a distance of 1,000 feet beneath a
neighborhood west of the site. Cleanup
activities have included removal of
stored chemicals from the site, limited
excavation of onsite soil, and removal
of all onsite buildings.
In 2001, the EPA began investigating
the possibility of vapor intrusion into
nearby homes. Air sampling performed
in homes around the CCI facility found
that VI raised concern for potential
exposure to some residents. TCE was
found to be the most prevalent VOC in
the groundwater and was detected
above the health-based action level in
several homes.
As a result of these findings, EPA
signed an action memorandum calling
for installation of VI mitigation systems
in homes near CCI. The Boeing
Company, one of several potentially
responsible parties, agreed to pay for
and install VI systems in those homes
identified by the EPA and to further
assess additional homes in other nearby
neighborhoods. Homes were selected
for sampling based on their proximity
to the CCI site and on the data
collected during site characterization.
Those with indoor air levels of target
substances above the action levels
(e.g., greater than 2 |lg/m3 for TCE)
qualified for a VI system. However,
residents had the option of turning
down installation of a system.
In total, indoor air was sampled in
more than 100 homes and VI systems
were installed in 45 homes (Figure 3).
The VI systems are the same as those
used to remove naturally occurring
radon in parts of Kansas. Acollection
pipe was placed on the ground
beneath homes with crawl spaces and
[continued on page 5]
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[continued from page 4]
vapor barriers were installed.
Vapors collecting in the pipe from
beneath the vapor barrier are
extracted with a fan and vented to the
outside via a vertical exhaust pipe that
discharges above the roof. Homes
with basements are vented to the roof
by placing the vertical pipe through the
concrete slab and into the subsurface.
The final remedy specified in a 2005
ROD includes a long-term VI
program as part of the overall
approach to groundwater remediation
at the site. Region 7 is responsible
for the O&M of the VI systems and
O&M work, which will be overseen
by Region 7, involves annual routine
inspections to verify that each system
is working properly. Before the first
inspection, the homeowner must sign an
access agreement that will allow EPA
and its contractors to enter the home to
perform O&M. The inspections take
note of any structural changes to the
home that may have occurred since
the installation of the VI system or
previous inspection which could impact
the effectiveness of the system.
In addition to O&M, the VI program
includes assessment sampling for
homes without VI systems, installation
of additional VI systems as necessary,
and performance monitoring of any
newly installed systems. The need for
additional assessment sampling will be
largely based on groundwater data,
which could indicate plume migration
LEGEND
• Homes Sampled at Least Once
ventilation System Installed During Interim Program
I * I Not Sampled in Interim Program I I Home
Because Access was Denied or
Owner Could Not Be Contacted •— - Business
Note: All properties were sampled
where access was granted.
into areas that have not previously
been tested.
Overall, the VI systems installed in
Olathe have been effective at
reducing contaminant levels to
levels below the EPA action levels.
Annual inspections have revealed
that most frequent problems involve
tears or rips in the membranes and
inadequate sealing around the edges
of the vertical pipes. Many of the
membranes have been replaced with
a heavier-duty material, and pipes
have been properly sealed. The
mechanical components generally
have had few problems. Because the
VI systems have a life expectancy
of 10-15 years, EPA anticipates the
need to periodically replace
mechanical components
such as fans as the
systems age over time.
Contributed by Mary
Peterson, EPA Region 7
(peterson.mary(a),epa.gov
or 913-551-7882)
Figure 3. EPA is responsible
for implementing the long-
term VI program at the site.
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Solid Waste and
Emergency Response
(5203P)
EPA 542-N-09-005
September 2009
Issue No. 44
United States
Environmental Protection Agency
National Service Center for Environmental Publications
P.O. Box 42419
Cincinnati, OH 45242
Presorted Standard
Postage and Fees Paid
EPA "
Permit No. G-35
Official Business
Penalty for Private Use $300
New Approaches Studied to Investigate Vapor Intrusion
In 2008, EPARegion 9 received an EPA
RARE grant (Regional Applied
Research Effort) to evaluate three
promising techniques for VI assessment
of indoor air: (1) using radon as a
surrogate for assessing VOC VI; (2)
using modified sorbent-based
methods for longer, time-integrated
measurements of indoor air VOCs; and
(3) using building pressure differentials
to assess the potential for VI. Available
indoor air analytical methods are
relatively expensive, so additional
research is needed to develop cost-
effective methods to evaluate vapor
intrusion into individual buildings.
Region 9's cross-program team in
collaboration with EPA's Office of
Research and Development is
comparing the results of the three
techniques with the goal of improving
and demonstrating cost-effective and
health-protective alternative approaches
for assessing vapor intrusion and
indoor air quality in homes and
commercial buildings. The EPA team
conducted concurrent field testing of
these methods at Orion Park Housing, a
vacated military residential area at the
Naval Air Station Moffett Field
Superfund site in California. Preliminary
data indicate promising results for longer-
duration, modified sorbent-based methods
for selected VOCs. The next phase of
the field work will focus on testing the
pressure differentials and active and
passive sorbent-based methods in
commercial buildings at NASA Ames
Research Center in California. Study
results are expected in 2010.
Contributed by Kathy Baylor,
Region 9 (baylor. katherine(a),epa. gov
or 415-972-3351)
Contact Us
Technology News and Trends
is on the NET! View, download,
subscribe, and unsubscribe at:
www.epa.qov/tio
www.clu-in.orq/newsletters
Contributions may be submitted to:
John Quander
Office of Superfund Remediation
and Technology Innovation
U.S. Environmental Protection Agency
Phone:703-603-7198
quander.iohn@.epa.qov
Call for Abstracts
EPA's Office of Superfund
Remediation and Technology Innova-
tion and the Environmental Institute at
the University of Massachusetts
Amherst recently issued a call for
abstracts of presentations at the
International Conference on Green
Remediation to be held in Amherst,
MA, on June 15-17,2010. Learn more
at: www.umass.edu/tei/conferences.
EPA is publishing this newsletter as a means of disseminating useful information regarding innovative and alternative treatment techniques and
technologies. The Agency does not endorse specific technology vendors.
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